Non-aqueous lithium ion electrochemical cells typically include an anode, a lithium electrolyte prepared from a lithium salt dissolved in one or more organic solvents and a cathode of an electrochemically active material, typically an insertion compound. During discharge, lithium ions from the anode pass through the liquid electrolyte to the electrochemically active material of the cathode where the ions are taken up with the simultaneous release of electrical energy. During charging, the flow of ions is reversed so that lithium ions pass from the electrochemically active cathode material through the electrolyte and are plated back onto the lithium anode.
Recently, the lithium metal anode has been replaced with a carbon anode such as coke or graphite intercalated with lithium ions to form Li.sub.x C. In operation of the cell, lithium ion passes from the carbon through the electrolyte to the cathode where it is taken up just as in a cell with a metallic lithium anode. During recharge, the lithium ion is transferred back to the anode where it reintercalates into the carbon. Because no metallic lithium is present in the cell, melting of the anode does not occur even under abuse conditions. Also, because lithium is reincorporated into the anode by intercalation rather than by plating, dendritic and spongy lithium growth does not occur.
Various factors influence the performance of electrochemical cells. For instance, the morphology of the polymeric matrix in the electrolyte layer and of the polymeric binders in the anode and/or cathode can affect conductivity of the salts. Enhancement of conductivity has been demonstrated by forming porous polymeric matrices and polymeric binders. One method of producing such porous structures comprises forming polymeric structures in the presence of a plasticizer; upon extraction of the plasticizer, pores are created in the polymer. Fillers are often added to improve the strength of the polymeric matrix. However, conventional fillers while strengthening the matrix comes at the expense of reducing cell performance. For example, fumed silica which is a common filler is thermodynamically unstable towards lithiated carbon. Specifically although fumed silica is treated so that silanol groups on the surface are replaced by hydrophobic groups, some unprotected silanol groups remain present. These silanol groups react with and consume lithium thereby reducing the amount of useful lithium.